Characterization of High‐Molecular‐Mass Forms of Basic Fibroblast Growth Factor Produced by Hepatocellular Carcinoma Cells: Possible Involvement of Basic Fibroblast Growth Factor in Hepatocarcinogenesis

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Abstract
Growth factor(s) with a strong mitogenic effect on BALB/c3T3 cells was purified from an extract of C‐Li21 cells, a human hepatocellular carcinoma line, by a combination of heparin‐affinity chromatography and reversed‐phase high‐performance liquid chromatography (HPLC). Two major peaks of mitogenic activity were obtained by reversed‐phase HPLC. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis analysis of the two peaks revealed that one was composed of three proteins with relative molecular masses of 27, 24 and 23 kilodaltons (kD), whereas the other was a single 19‐kD protein. Immunoblot analysis showed that all four of these molecules were immunoreactive species of human basic fibroblast growth factor (bFGF). N‐Terminal sequence analysis of these molecules revealed that most of them were N‐terminally blocked. However, small proportions of the 23 and 19‐kD molecules were not blocked, and their respective N‐terminal sequences were found to correspond to Gly ‐40‐Gl‐27 and Pro29‐Phe40 of human bFGF deduced from the cDNA sequence of a human hepatoma cell line, SK‐HEP‐1. Expression of bFGF in hepatocellular carcinomas was then investigated by RNA blot analysis. All of the examined hepatocellular carcinoma cells expressed bFGF, and the degree of expression was higher in surgically resected hepatocellular carcinomas than in the corresponding adjacent non‐cancerous liver tissue. Transcripts of bFGF were not detected in normal liver. These results suggest that C‐Li21 cells produce four molecular forms of bFGF, and that bFGF may be involved in hepatocarcinogenesis. Moreover, it appears that bFGF is a potent mitogen toward primary‐cultured hepatocytes, and that high‐molecular‐mass forms of bFGF produced by C‐Li21 cells have stronger mitogenic effects on hepatocytes and are more stable under acidic conditions than the low‐molecular‐mass form, composed of 146 amino acids.